# Observation of symmetry-protected topological band with ultracold fermions

## TL;DR

This paper reports the experimental observation of a symmetry-protected topological band in ultracold fermions within a one-dimensional optical lattice, highlighting the role of symmetry in topological phases and their dynamics.

## Contribution

It demonstrates the realization of a noninteracting SPT band protected by magnetic and chiral symmetries in ultracold atoms, and explores quench dynamics between topologically distinct regimes.

## Key findings

- Observation of a symmetry-protected topological band in ultracold atoms
- Distinct spin dynamics observed in quenches to trivial and nontrivial regimes
- Topological properties confirmed via Bloch states at symmetric momenta

## Abstract

Symmetry plays a fundamental role in understanding complex quantum matter, particularly in classifying topological quantum phases, which have attracted great interests in the recent decade. An outstanding example is the time-reversal invariant topological insulator, a symmetry-protected topological (SPT) phase in the symplectic class of the Altland-Zirnbauer classification. We report the observation for ultracold atoms of a noninteracting SPT band in a one-dimensional optical lattice and study quench dynamics between topologically distinct regimes. The observed SPT band can be protected by a magnetic group and a nonlocal chiral symmetry, with the band topology being measured via Bloch states at symmetric momenta. The topology also resides in far-from-equilibrium spin dynamics, which are predicted and observed in experiment to exhibit qualitatively distinct behaviors in quenching to trivial and nontrivial regimes, revealing two fundamental types of spin-relaxation dynamics related to bulk topology. This work opens the way to expanding the scope of SPT physics with ultracold atoms and studying nonequilibrium quantum dynamics in these exotic systems.